Ultra high frequency apparatus



May 23, 1950 s. sENslPER ULTRA HIGH FREQUENCY APPARATUS Filed March 22,1946 f* il#l INVENTOR` 5A UEL SENS/PER m/ ATTl ORNEY Patented May 23,1950 UNITED.. STATES ULTRAHIGH FREQUENGY `IAPlAmi'iUsffI SamuelSensiper, Garden City; N. .Intassignor vkto. The Sperry I Corporation;a. corporationvolllelay,

Application March 22, 1946;.'SeriaPN0s7658202 13 Claims. (Cl.'.178,-44)v,

Therpresent invention-relates "to devices operating; at ultra-highfrequenciesrand Isuper-higlrY frequencies and Iespeciallyto`attenuatingv ldevices adapted for use in'. concentric transmission;yline systems.

It is well known that a, hollow-pipe"waveguide, while. ane'icientconductcrz of electromagnetic energy whoseWavelengthiis-lessfthan a criticalv value known as cut-01T Wavelength,determined by the. internal transversedimensions of the` guide, is A an.excellent attenuatorri` of electromagnetic energyA provided.: thewavelength of the energy is greater than icuteoi.' As an example of therelative valuesofthe attenuatiomabove and.Y below cut-offwavelengtm-anair-nlledhollow` conductive pipe of f threeffinches insidediameter.

will conduct electromagnetic" energy having "a Wavelength shorter'vthanafive 4inches with `an atv tenuation` constants.: smaller-r thanone-tenth decibel per foot'of Ilength of the'wave guide. This sameguide, on :the'foth'erzhandg: attenuates-e1ec.

tromagnetic energy'4 l01E Wavelength'r appreci-alolyY greater thanveinches `by an `attenuationiconstant greater than 120"deciloe1slper=footfof `length of the wave guide.

It is this'property of hghattenuationfper 'unit length of waveguidedimensioned to avfrequencyf below eut-'oiifl that makes itz-tusefulasfan'u1tra+ high-frequency .-attenuator: While'v it fWould be possible toconstruct various lengths of suchfwave guide which couldbeinsertednatransmission` line system and thusgivethe 'desired attenuation;

it is more desirable from a practicalrstandpoint tol design theattenuator so'that its total -attenuationV maybe variedfas desired.Another cdesirable'ffeature=isthat athefattenuationvary flinearlywitlrany displacement"ofthecontrolfnrrechanism.y Severalconstructionsfof fsuchfvariable attenuators -havebeenv suggested'fandftried:A AccordingY toV one such f construction; electromagnetic energyVis :intro-v ducedinto one: end cf azlengthf offwavefguide whosetransverse dimensions; make w-it belowf-cutoi at theoperatingffrequency-v and suchenergyz is-:picked upvbyrfa r looporIotherV -form :of pickup device- Wh'ich" fis Emovable@inside the device.The

attenuation varieswith1thefdistance -between the source for@ inputcoupling-of the-electromagneticenersyf andnthelpickup device.

in whichithefattenuation variesiinearlyfwithdistancebetweeniinputzandzpickup; hasbeen limited;

Thei cause of lthissfrestrictedrange `has' been lthat priorL energyA'sourcesfhave f-tendedfpgto, excitegf the: waveffguide in several'diierentmodesiofpropaga tion, mosti-offwhieh attenuate =quitezrapidlywith=A 55y toga; section of coaxial-@line Y distanceffrom thesource; orderrrorfthez picke trbute: energyiv Thusypriorf deviceswereflinearfg only in that portion ofthefzwave, guidebeyondf whichcmore.-A than-oneemode @existed in any: `,apprecialoledegrees1l Sinceit@is-w oni-y the flinearfranger ofrthecwate. tenuator which isuseful':any.lattenuation,which exists at @the .lowu end offtheattenuatorstuseul ranges-is:fconsideredfas .a1oss,; usually,ftermedfFan/*f insertion -lossY-v: In many appl-icationsfinwhich1`sucheafvariable,:attenuator f-isi=,used-. rin an .-ufltra-fAhighgfrequencyesystem, the{source-aofithei'ultragf highfrequencyieneigymay be slir-nited-` inapowerA output.-v Forthisfreascnyit-ishighlydesirablefthat suchrflossesebeskepttofaefveryyminimum:y Sucht insertion loss is theratio-:(expressedin decibels` ofYthevpower:delivered'beioreethe insertionY of fthe attenuatorxinto^thesystem to-the power del-ivered after r the f attenuatorfs:insertion withi themr at. tenuator fadjusted-to sminimumfattenuationitx-its?l useful .range-5 Inipr-ior, variabieaattenuators; :thiskinsertionglossis has :had f a fvalue-rimthe Vneigl'foor--w hood of 45decibe1s.f.,1noneformiof aiftenuator.t madem-in .faccordancefw-ith-thepresentinvention, thisfvaluefhas-been'reduced towapproximatelyy'Z-decibels'.A

Af; principal-obi ect-of.=l the-@presentfinvention isay to provideimprovedapparatus-for exciting-f ayvvavev guide in which excitation isminimizedrinfeu lbut a-f-singie :predetermined-mode:

It is a furtherf ohjeci' ofthe present :inventionn toprovidezfapparatusforiexeitingal, Wave guide isfprovidedjasection,l L01E awaverguid'e'fdimensonedf belowr'fcutfofiwhlchis.couple iaiaenoveLi-Iashionr whlcheitissue-1' Vof coupling'` loop cited. The novel coupling consists of arectanof the coaxial line considerably reduces insertion The inner Wallof the outer conductor of loss. the line is tapered so as to lead up tothe flat plate without introducing any sharp discontinuity into the wallof the coaxial line. The tapering thus prevents undesirable wavereflectionsl that would occur if the end of the wave guide aloneprotruded into the coaxial line.

The combination of wave guide insertion and side wall tapers furtherresults in an extended frequency range in which the standing wave ratiois small. Such a frequency range is termed the ."bandwidth of theinstrument. A movable cou-` members to the sides of the movablecouplingV loop.' Such members short out the electric field ofundesirable modes which may exist in the wave guide-while having noeffect on the desired mode(` excited by the rectangular slot.

VThe invention in another of its aspects relates to novel features ofthe instrumentalities described herein for achieving the principalobjects of the invention and to novel principles employed in thoseinstrumentalities,.Whether or not these features and principles are usedfor the said prin- 'eipalobiect or inthe said field.

Afurther object of the invention is to provide improved apparatus and.instrumentalities embodying novel features and principles, adapted foruse'in realizing the above objects and also adapted-for use in otherfields.

In the drawings: Y

Fig. l is a plan view, partly in section of one embodiment of thepresent invention; l

Fig. 2 visv a fragmentary cross-sectional view takenfalong line A -A inFig. l which shows the rectangular slot;

* Fig. 3 isa cross-section of an ordinary coaxial4 line 4withconventional electric field conguration', as at line B-B of Fig. 1. Y

Fig. k"4 is a fragmentary cross-section taken along line `C-C of'Fig. 1showing the electric eld configuration at this point; and I Fig. 5 is-aVperspective view of a modied form used Vinthe embodiment shown inFig. 1. Y

' In Fig. 1 is shown a plan Yview'of'an embodiment of the presentinvention. A section of Wave guide I Il dimensioned below cut-off in theoperatlng frequencyrange is inserted in T fashion into' coaxial line IIthrough which ultra-high-frehaving center conductor I3 supported by anywell known broad-bandisupport such as the conv'elb 4 tional T stubsupport I4 within an outer conductor I5. If it is desired, a powermonitor may be connected to the opposite end I9 of the coaxial line I Iby means of threaded connection 20. This permits a measure of theabsolute power'level of the ultra-high-frequency energy before it isattenuated. An input-matching resistor disc 2l is provided near the endI9 yof Vthe coaxial line II. The purpose of this disc 2| is to match theinput impedance of the lattenuator looking down the Vcoaxial line I I atthe end I2 with the microwave transmission system into which theattenuator is inserted. Y

The end of Wave guide I Il which protrudes through the outer conductorI5 of the coaxial line II is terminated in a flat plate I6 whichcontains a rectangular slot Il extending perpendicularly to innerconductor I3. This flat plate I5 is positioned close to center conductorI3. Wall tapers I 8 which lead up to flat plate I6 are provided on theinside wall of outer conductor I5's0 as to prevent va sharpdiscontinuity 4 which would cause reflections in the coaxial lineresulting in an nndesirablefhigh standing Wave ratio which wouldincrease the insertion loss.

Mounted inside wave guide I0 is a movable pickup loop 29. One end ofthis pickup loop 29 is fastened to the inner Wall of a tube 22 whichslides telescopically inside the wave guide I0. The

remaining end ofpickup loop 29 extends 4axially down tube 22 to form acenter conductor 23 of a coaxial line formed by tube 122 and centerconductor 23. Approximately one-quarter of a Wavelength down the centerconductor 23 away from pickup loop 29 a matching resistor disc 5E! isprovided to match the output impedance of the attenuator to the systemswith which it is to be connected. An outer tube.24, which surrounds waveguide I0, can be moved in translation by means of knob 25 fixed to apinion 25' which interacts with rack 2B fastened to tube 24. Thistranslation of tube 24 is transferred to tube 22 by means of screw 21which passes through a slit 28 lin wave guide II] and engages tube 22.Thus, by rotation of knob 25, outer tube 24, tube 22, loop 29 and centerconductor 23 moveY in translation as a unit. Sucnmovement varies thedistance between exciting slot I'I and coupling loop 29. As can readilybe seen from Fig. 1, the length of Wave guide I0 that is used totransfer energy is just the distance between slot II and loop 29, as thesystem becomes anormal coaxial transmis'- sion line beyond loop 29. Itis this length of wave guide ID which provides the attenuation.

Since the coaxial line that is formed by tube 22 and centerV conductor23 is smaller in crosssection than the standard coaxial line II, it isnecessary to provide transition units in order to bring the dimensionsof the inner and outer conductors up to the vstandard size. It is alsonecessary to provide a telescoping joint for the center conductor 23 toallow for its translatory motion. Step-types of transition units tareshown at 30 and 3 I. As is seen at 30, a short section of coaxiallinelis provided with increased dimensions by a step or increase incross-section 32 in the center conductor 23 and a similar step 33 in theouter conductor or tube 22. In making such steps it is necessary thatthe ratio of the inside diameter of the outer conductor to the diameterof the inner conductor be kept constant so that the characteristicimpedanceof the line, which is a function of thisY ratio, does notchange. Furthermore, these changes must be made in small steps so -asnot to set up `any local eld effects at the.

step which would cause reections to be set up in the coaxial line. Toremove any capacitance eiects that may be introduced by the steps, it iscustomary to make the length of the transition units or stepsapproximately one-quarter of a wavelength of the energy which the deviceis designed to attenuate. In this way the capacitance effects introducedby one stepA are cancelled by the capacitance eiects introduced by thesecond step a quarter of a wavelength further along the line. Stepssimilar to 32 are shown at 34, 35 and 36 with the distance betweensuccessive steps of each pair being approximately one-quarter of awavelength. The last of these steps 36 provides a transition to coaxialline 31 which is of standard size and allows a standard output connector44 to be provided at the end of the coaxial line 31.

If it so happensy that the impedance of the coaxial line having thesmallerv dimensions differs from the impedance of the standard output coaxial line, such transition units not only serve to provide steps forincreasing the coaxial line dimensions but also allow for a gradualimpedance transformation. In such a case the characteristic impedance ofany transition unit is so designed so as to be equal to theroot-meamsquare of the characteristic impedance values oi the two lineswhich it connects.

An alternative type of transition unit is the familiarcoaxial taperedsection. In this type of transition unit both the inner and outerconductors are enlarged in a tapered section, care being taken as in thestep type of transition unit, that the ratio of the outer conductordiameter to inner conductor diameter be kept constant so that theimpedance of the line does not change.

The center conductor 38 of coaxial line 31 has a bore 39 at one end.This bore 33 receivesk the enlarged end section 45 of the centerconductor 23` and enables movement of the same in translation.

In operation, ultra-high-frequency energy is introduced at end I2 ofcoaxial line I I. The electric eld that is thus set up between the innerconductor I3 and the outer conductor I5 excites the rectangular slot I1which in turn excites the wave guide IU. Energy is transferred by way ofwave guide I to the pickup loop 29 which couples the energy to thecoaxial line -formed by the center conductor 23 and outer conductor 22.This energy is transmitted through coaxial line 31 to the standardcoaxial fitting dii. Sincel wave guide I0 is dimensioned below cut-offfor the ultrahigh-frequency energy that is introduced into coaxial lineII, it attenuates this energy as it is transferred to pickup loop 29.The arnountfof attenuation is determined" by the length of the transferpath between resonant slot I1 and pick*- up loop 29. Therefore, as theknob 25 is rotated and the pickup loop 29 is moved awayl from recetangular slot I1, the length of the wave guide I0 thatis used isincreased, thereby increasing the total attenuation.

The advantage of bringing the end ofl wave guide I0' close to the'centerconductor I3 is readily seen' by reference to Figs. 3 and 4'. In Fig. 3we see the cross-section of a conventional coaxial line with the arrows4U representing the electric ield conguration. As is well known, if theinner and outer conductors I3l and I5 are both circular in cross-sectionand are concentrically placed, the electric iieidy will be radial and'uniform around the axis of the coaxial line at any given distancev awayfrom the' centerv conductor.

If we" nowirefer' tovF'g. 4 we seerv thatv the situation is changedconsiderably. Instead of a uniform eld, there is a concentration of theelectric 'iield in the region of slot I1, due to the proximity of plateI 6 which contains slot I1 to the center .conductor I2. It is thisconcentration of the electric leld in the region of the rectangularslotI1 'which excites the wave guide Iii in such an eicient manner thusreducing the insertion loss from the usual figure of Li5 decibels toapproximately 25 decibels. Care must be taken, however, that reiiectionsare not set up in coaxial line I I by the insertion of the end of waveguide Iii through the outer conductor I5. Such reflections would resultin a high standing wave ratio with a resulting increase in insertionloss. To prevent such reiie'ctions, the `wall tapers I8 are built intothe inner wall of the outer conductor i5. These wall tapers I8 lead the'inner wall up to the ilat plate Iin a gradual slope without introducingany sharp discontinuity in the conducting surface. In one embodiment ofthis invention the length of these tapers I8' may 'be approximatelyone-half of a wavelength at the wavelength of the approximate center ofthe band for which the attenuator is designed. The combination of tapersI3 and the reduction in distance between center conductor I3 andexciting slot I1 not only lowers the insertion loss, as mentioned, butaids considerably in improving the bandwidth of the device. As mentionedpreviously, bandwidth is the frequency range over which the instrumentwill operate and still maintain a small standing wave ratio.

The advantage in. using slot excitation of the 'cut-off Wave guide is inthe reduction of multiple mode excitation; that is, the energy whichpasses through the wave guide I is predominantlyof a single mode.Reference to Fig. 2 which is a cross-section taken along line A-A ofFig. 1

shows rectangular slot I1. By virtue of the rectangular shape of thisslot I1, a mode of the TEii type is predominantly excited in the Waveguide `Iil having an electric field coniiguration li3 as is shown bydotted lines in Fig. 2. This type of slot minimizes excitation of modesother than the 'IEn mode. As pointed out previously the advantage ofunimodal excitation is that the energy which is transferred down thewave guide In is attenuated substantially linearly with increase i-n thedistance between the rectangular slot I1 and the pickup loop 29. Withmultiple-mode excitation this is not the case, since each mode that isexcited has its individual attenuating chan acteristics with respect todistance along the wave gllide, and the pickup device 29 responds at anygiven point along the wave guide to the sum oi the electricfields due toeach of the modes excited. From the foregoing, it is apparent that itisonly' in the region beyond which more. than oneV model exists thaty theattenuator varies linearly with displacement of the pickup loop 29.Thus, slot excitation of the present typeaids in extending the region oflinearity ofv the attenu- 'ator".

' It should be noted that any improvement or extension in linearity byminimizing extraneous modes allows the minimum usable value ofattenuation to be lowered. Thus, the insertion loss of the attenuator isdecreased by an increase in linearity.

A further improvement in linearity of the at@ tenuator and reductionofinsertion loss may' be obtained by a modiiication of the pickup loop 29.It is readily understood that if the pickup loop 29'- could be somodifi-ed that it would respond to the desired mode existing in thewave` guide' I0 and at the same time minimize-itsresponse toundesirableV modes that mightexist, the overall performance of theattenuator would thus be improved. Such a modication of the couplingloop 29 is shown in Fig. 5. In this modification, the coupling loop 29is provided with arms or wings 46 which extend radially from the centerconductor 23 in the plane of coupling loop 29 and at right angles to it.These wings 46 may or may not touch the wall of the outer conductor 22,as desired. Such wings 46 serve to short out or kill any electric Iieldconfiguration which has a component along their axis. Since the electriciield configuration of the desired mode which is excited by therectangular slot I1, shown by dotted lines in Fig. 2, is normal to theaxis ofv such wings 46, it remains unaiected by their presence. Hencethe wings 46 cause loop 29 to respond only to a single mode ofexcitation of wave guide l0, even if other modes should be excitedtherein, and improve correspondingly the performance of the attenuatorwith respect to linearity, insertion loss, and bandwidth.

Although the presenti invention is shown embodied in anultra-high-frequency attenuator, it should be understood that such acoupling device will work equally well in any instrument or transmissionsystem in which it it desired to couple a coaxial line to a wave guidein which it is desired that but one predominating mode be excited or bepicked up.

Since many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1.'Apparatus for variable attenuation of electromagnetic energycomprising a section vof co' axial line through which said energy isadapted to be conducted, a wave guide with cross-sectional dimensionstoo small for efficient transmission of said energy in the band ofoperating wavelength, v

said wave guide communicating with said coaxial line and having an endprotruding through the outer conductor of said coaxial line but spacedfrom the inner conductor of said coaxial line,

means for coupling said coaxial line to said wave guide, said meanscomprising a flat plate mounted across said inwardly protruding end ofsaid wave guide, said flat plate having a rectangular slot therein,extending perpendicularly to said coaxial line, means for preventingenergy reflections in said coaxial line due to the protrusion of saidend of said wave guide into the outer conductor of said coaxial line,said means comprising tapered conductive members leading from the innerwall of the outer conductor of said coaxial line to the said at plateand removing discontinuities in said coaxial line, means for extractingsaid energy having but a preferred plane of electric field orientationin saidA wave guide, said means comprising a coupling member oriented soas to couple with said energy having said eld orientation and aplurality of shorting members oriented at right angles to said couplingmember and mounted in a plane normal to the direction of energy transferin said wave guide, said shorting members serving to short-out anyelectric eld having a component normal to the axis of said couplingmember, and means for varying the .longitudinal position of saidenergy-extracting 8 means, whereby the length of said hollow wave guidebetween said rectangular slot and said energy extracting means isvaried, causing variation in the attenuation of said energy.

2. Apparatus for Variable attenuation of electromagnetic energy,comprising a section of coaxial line through which said -energy isconducted, a wave guidedimensioned below cut-off in vthe band ofoperating wavelengths, said wave guide communicating with said coaxialline and having an end protruding through the outer conductor of saidcoaxial line but spaced from the inner conductor of said coaxial line,means for coupling said coaxial line to said wave guide, said meanscomprising a thin conductive member mounted across said inwardlyprotruding end ofsaid wave guide, said member having an opening therein,means for preventing energy refiections in said coaxial line due to theprotrusion of the end of said wave guide into the outer conductor ofsaid coaxial line, means for extracting said energy having but apreferred plane of electric field orientation in said wave guide, saidmeans comprising a coupling member oriented so as to couple with said-energy having said field orientation and a plurality of shortingmembers oriented at right angles to said coupling member and mounted ina plane normal to the direction of energy transfer in said wave guide,said snorting members serving to short out any electric eld having acomponent normal to the axis of said coupling member, and means forvarying the position of said energy extracting means, causing variationin the attenuation of said energy.

3. Apparatus for variable attenuation of electromagnetic energycomprising a section of coaxial line through which said energy isadaptedto be conducted, a wave guide of cross-sectional dimensions toosmall for efficient transmission of said energy in the band of operatingwavelengths, said wave guide communicating with said coaxial line andhaving an end protruding through the outer conductor of said coaxialline but spaced from the inner conductor of said coaxial line, means forcoupling said coaxial line to said wave guide, said means comprising aflat plate mounted across said inwardly protruding end of said .waveguide, said flat plate having a rectangular slot therein extendingperpendicularly to said coaxial line, means for preventing energyreections in said coaxial line due to the protrusion of the end of saidwave guide into the outer conductor of said coaxial line, said meanscomprising tapered conductive members leading from the inner wall of theouter conductor of said coaxial line to the said fiat plate and removingdiscontinuities in said coaxial line, means for extracting said energyfrom within said Wave guide, and means for varying thel longitudinalposition oi said energy-extracting means, whereby the length of saidwave guide between said rectangular slot and said energy-extractingmeans is varied, causing variation in the attenuation of said energy. l

4. Apparatus for Variable attenuation of electromagnetic energycomprising a section of coaxial line through which said energy isadapted to be conducted, a wave guide of cross-sectional dimensions toosmall -for eiiicient transmission of said energy in the band ofoperating wavelengths, said hollow wave guide communicating with saidcoaxial line and having an end protruding through the outer conductor iof said coaxial line but spaced from the inner-conductor ovfsaidvcoaxial line, means for coupling s aid caxi'al' line to" said waveguidesaid means come prising' a fiat plate mounted across said inwardlyprotruding end of said wave guide,` said flat plate having a slottherein,- means for preventing energ-y reflections in said coaxial linedue to the protrusion of the end of saidv wave guide into the outerconductor of said coaxial line, said means comprising tapered conductivemembers leading from the inner wall of the' outer condlictoi f saidcoaxial lin'e" to the Said iiat plate and removing discontinuities insaidcoaxial line, means for extracting said energy from within said Waveguide', and means for varying the' longitudinal position of saidenergyi'e'xtracting means, wherebyv the length of said wave guidebetween 4said slot and said energy-extracting means is varied, causingvariation in the attenuation of said energy. v

5. Apparatus for variable attenuation of electromagnetic energycomprising a section of coaxial line through which said energy isadapted to be conducted, a wave guide dimensioned below cut-off in therange of operating wavelengths, said wave guide communicating withsaidcoaxial line and havingan end protruding through the outer conductorof said coaxial line but spaced from theinnergconductor of said coaxialline, means for coupling said coaxialline to said wave guide, said;means comprising a nat plate-'mounted across said inwardly protrudingend of said wave guide, said flat plate having an opening therein,meansv for preventing energy reflectionsl in s aid coaxial line due tothe protrusion4 of the` end oi said wave guide into the outer conductorof said coaxial line, said means comprising tapered conductive membersleading from the inner wall of the outer conductor of said coaxial lineto the said flat plate and removing discontinuities in said coaxialline, means for extracting said energy from within said wave guide, andmeans for varying the longitudinal position of said energy-extractingmeans, whereby the length of said wave guide between said opening andsaid energy-extracting means is varied, causing variation in theattenuation of said energy.

6. Apparatus for variable attenuation of electromagnetic energycomprising a section of coaxial line through which said energy isadapted to be conducted, a wave guide dimensioned below cut-oit in therange of operating wavelengths thereof, said wave guide communicatingwith said coaxial line and having an end protruding through the outerconductor of said coaxial line but spaced from the inner conductor ofsaid coaxial line, means for coupling said coaxial line to said waveguide, said means comprising a thin conductive member mounted across theinwardly protruding end of said wave guide, said conductive memberhaving an opening therein, means for preventing energy reiiections insaid coaxial line due to the protrusion of the end of said wave guideinto the outer conductor of said coaxial line, said means comprisingtapered conductive members leading from the inner wall of the outerconductor of said coaxial line to the said thin member and removingdiscontinuities in said coaxial line, means for extracting said energyfrom within said wave guide, and means for varying the longitudinalposition of said energy-extracting means, whereby the length of saidwave guide between said opening and said energy-extracting means isvaried, causing variation in the attenuation of said energy.

7. Apparatus for variable attenuation of electromagnetic energycomprising a section of co- 1Y0 axial line through which said energy isadapted to be conducted, a wave guide of cross-sectional dimensions toosmall for eiiicient transmission of said energy in the range ofoperating wavelengths thereof', said wave guide communicating with saidcoaxial line and having an end protruding through the outer conductor ofsaid coaxial line but spaced from the inner conductor of said coaxialline, means for coupling `said coaxial line to said Wave guide, saidmeans comprising a thin conductive member mounted across the inwardlyprotruding end of said wave guide; said thin conductive member having anopening therein, means in said ccoaxial line for preventing energyreections due to the protrusion of the end o1"- sa-id wave guide intothe outer c'o'nductor of said coaxial line, said means comprising a;tapered conductive structure extending from the inner wall of the outerconductor of. said coaxial line to the periphery of said thin member;Vthereby eliminating discontinuities the coaxial line, meansV forextractingI said 'en-V ergy from within' said wavel guide, and means'for varying the longitudinal position of sai'c'll energy-extractingmeans, whereby the length of said wave guide between said opening andsaid energy-"extracting means is varied',y causing variation in theattenuation of said energy.

8; Apparatus for variable attenuation of .elec`A tromagrietic energycomprising a section of coaxial line through which said energy is?adapted to'y be conducted, a wave guide of cross-sectional dimensionsbelow cut-off; said wave guide com'-- municating with" said ,coaxialVline andf having? an end protruding through the outerl conductor of saidcoaxial line but spaced from the inner conductor of said coaxial line,means for coupling said coaxial line to said wave guide, said meanscomprising a thin conductive member mounted across the inwardlyprotruding end of said wave guide, said thin conductive member having anopening therein, means for preventing energy reflections in said coaxialline due to the protrusion of the end of said wave guide into the outerconductor of said coaxial line, said means comprising tapered conductivemembers leading from the inner wall of the outer conductor of saidcoaxial line to the peripheral portion of said thin conductive member,means for extracting said energy from within said wave guide, and meansfor varying the position of said energyextracting means causingvariation in the attenuation of said energy.

9. Ultra-high-frequency apparatus for coupling a coaxial line and a waveguide communicating with said coaxial line and having an end protrudingthrough the outer conductor of said coaxial line but spaced from theinner conductor oi said coaxial line, said apparatus comprising a hatplate mounted across the inwardly protruding end of said wave guide,said flat plate having a rectangular slot therein extendingperpendicularly to said coaxial line and means for preventing energyreections in said coaxial line due to the inwardly protruding end ofsaid wave guide, said means comprising tapered conductive membersleading from the inner wall of said coaxial line to said flat plate.

10. Ultra-high-frequency apparatus for coupling a coaxial line and awave guide communicating with said coaxial line and having an endprotruding through the outer conductor of said coaxial line but spacedfrom the inner conductor of lsaid coaxial line, said apparatuscomprising a flat plate mounted across the inwardly protruding end'ofsaid wave guide, said at plate having a slot therein, and means forpreventing energy reflections in said coaxial line due to the inwardlyprotruding end of said wave guide. said means comprising taperedconductive members leading from the inner wall of said coaxial line tosaid :fiat plate. Y

11. Ultra-high-frequency rapparatus for couplinga coaxial line and awave guide communieating with said coaxial line and protruding throughthe outer conductor of said coaxial line, said apparatus comprising aflat plate mounted across the inwardly protruding end of said waveguide, said flat plate having an opening therein, and means forpreventing energy reections in said coaxial line due to the inwardlyprotruding end of said wave guide, said means comprising taperedconductive members leading from the inner wall of said coaxial line tosaid flat plate.

12. Ultra-high-frequency apparatus for coupling a coaxial line and awave guide communicating with said coaxial line and protruding throughthe outer conductor of said coaxial line but spaced from the innerconductor of said coaxial line, said apparatus comprising a thinconductive member mounted across the inwardly protruding end of saidwave guide, said member having an opening therein, and means forpreventing energy reflections in said coaxial line due to the inwardlyprotruding end of said wave guide, said means comprising taperedconductive members leading from the inner wall of said coaxial line tosaid member. 13. Ultra-high-frequency apparatus for coupling a coaxialline and a wave guide communicating with said coaxialline and protrudingthrough the outer conductor of said coaxial line but spaced from theinner'conductor of said coaxial line, said apparatus comprising a thinconductive member mounted across ,the inwardly protruding end of saidwave guide, said member having an opening therein, and means forpreventing reections in said coaxial line due tothe inwardly protrudingend of said Wave guide, said means comprising tapered conductive membersextending from the inner wall of the outer conductor of said coaxialline to the peripheral portion of said thin conductive member, therebyeliminating discontinuities in the line.

SAMUEL sENsIPER.

REFERENCES CITED The following references are of record in the file ofthis patent:

Linder July 1, 1947

